1. Field of the Invention
The present invention relates to a plate-link chain, in particular for a motor vehicle drive system, wherein the chain includes a large number of link plates that a pivotally connected with each other via rocker members,
2. Description of the Related Art
In known plate-link drive chains the rocker members run transversely to the longitudinal direction of the chain and are positioned in openings provided in the link plates. There are curved contact surfaces situated on each of the rocker members and on opening surfaces of the link plates, along which contact surfaces the rocker members and link plates are in contact with each other to transfer power. The contact surfaces between rocker member and link plate are provided at upper and lower contact surface regions in the height direction of the rocker member, the opening in the link plate having at least one region that is curved in an inward direction.
The rocker members also have curved rolling surfaces, along which contacting rocker members roll against each other to transfer power. Further, the rocker members are shaped asymmetrically in the height direction of the rocker members, when viewed in a cross section extending in the longitudinal direction of the chain.
Such a known plate-link chain can be a toothed chain, which can be employed in a power divider transmission of a motor vehicle, for example, or as a drive chain for an auxiliary unit of an internal combustion engine of the motor vehicle. The plate-link chain can be designed as a toothed chain to transmit tractive force between a driving and a driven chain wheel. But a plate-link chain of the general type described above can also be employed as a means of transmitting tractive force in a belt-driven, conical-pulley transmission, or the like, for example, and can there transmit the tractive force by means of frictional contact between the ends of the rocker members and the conical disk surfaces of the two conical disk pairs.
A plate-link chain designed as a toothed chain normally includes a device for tensioning the toothed chain in the slack strand. The device for tensioning the toothed chain serves to prevent pulsating of the toothed chain due to vibration excitation, for example, and also to shape the entry process of the teeth of the toothed chain onto a chain wheel so that tooth skipping is prevented. On the chain wheels the toothed chain is deflected in such a way that the center of curvature of the portion of the toothed chain that is curved in the region of the deflection lies within the closed chain section.
In contrast, when a chain tensioner is in the form of a chain tensioning bar acting on the back of the link plates, for example, the toothed chain undergoes a curvature that differs from the curvature that occurs in the region of the deflection. The particular portion of the toothed chain that is acted on by the chain tension is curved in the opposite direction, and the center of curvature of that portion of the toothed chain lies outside of the closed chain section of the plate-link chain.
To limit the deflection angle of that swing-back mode from the stretched position, in known versions of plate-link chains for belt-driven conical-pulley transmissions, for example, and in toothed chains, there is provision for limiting the swing-back in the joint of the lower region of an adjacent link plate.
The mode of functioning here is such that a rocker member comes into contact with a region of the lower contact surface of the adjacent link plate. Thus the striking of the rocker member on the contact surface of the adjacent link plate occurs in a region that is already critically loaded in any event, due to the transmission of tensile force from the rocker member to the link plate. Hence, in the region of concentrated tension due to the transmission of tensile force, yet another additional overlay of forces occurs, and thereby also tension due to the swing-back protection. In the operation of the toothed chain that arrangement can result in increased wear and ultimately to early fatigue failure. The fatigue strength of the toothed chain is thus reduced.
Plate-link chains that were known in the past had symmetrical rocker members that were situated in openings in the link plates. Those known rocker members are symmetrical in construction in reference to a plane of symmetry that divides the rocker members into an upper and a lower half. As a result of that configuration, a distance from the inner peripheral rim of the link plate opening that receives the rocker members, to an outer peripheral edge of the link plate in the region of a so-called lower yoke is made smaller, and thus the cross-sectional region available for transmitting force is reduced in size.
In consequence, a concentration of stress appears in the region of the link plate between the opening of the link plate and the edge of the link plate, which ultimately results in a reduction of the service life and of the force-transmitting capability of the plate-link chain. To counter that problem, a plate-link chain is known that has asymmetrical rocker members in the direction of the rocker member height, and thereby ensures that the workpiece stresses that arise in the upper and lower contact surface regions between rocker member and link plate are significantly reduced, so that the service life of the chain is increased as a result.
With a plate-link chain of that type it is important that the asymmetrical rocker members are inserted into the openings in the link plates in the correct orientation, since otherwise the rolling surfaces of the rocker members that are intended for transmitting force cannot roll against each other as intended. As a result, jamming of the rocker members in the link plate opening can occur, and thus a malfunction that can result in failure of the plate-link chain.
To achieve the correct orientation of the rocker members in the link plate openings, a plate-link chain is disclosed in unpublished German patent application DE 10 2005 061 081.1. In that chain the link plates have a region in the plate opening that is curved in an inward direction, so that if the rocker members are oriented incorrectly an overlapping of the outside contour of the rocker members with the inside contour of the plate opening occurs, and the rocker member that is not in the correct orientation can no longer be inserted into the link plate opening. In that way erroneous installation of the rocker members in the openings of the link plates is avoided.
It has been found that that known plate-link chain already provides an improvement, compared to the plate-link chain described previously, in regard to additional stress at the stress-critical region in the region of the lower loop of the link plate. But even that known plate-link chain has room for improvement in regard to the stress in the described stress-critical region to protect against swing-back due to the striking of the rocker member on a contact surface of an adjacent link plate.
Consequently, an object of the present invention is to refine the known plate-link chain in such a way that the force applied to the plate-link chain due to the striking of the rocker member on the link plate to limit the swing-back angle takes place in a less tension-critical region along the link plate opening.